Description: The West Antarctic Peninsula (WAP) is a climatically-sensitive region where periods of strong warming have caused significant changes in marine ecosystem and food web processes. Tight coupling between phytoplankton and higher trophic levels implies that the coastal WAP is a bottom-up controlled system, where changes in phytoplankton dynamics may largely impact other food web components. Here, we analyzed the interdecadal time series of year-round chlorophyll-a (Chl) collected from three stations along the coastal WAP, Carlini Station at Potter Cove (PC) on King George Island, Palmer Station on Anvers Island, and Rothera Station on Adelaide Island. There were trends toward increased phytoplankton biomass at Carlini Station (PC) and Palmer Station, while phytoplankton biomass declined significantly at Rothera Station over the studied period. The impacts of two relevant climate modes to the WAP, the El Niño-Southern Oscillation and the Southern Annular Mode, on winter and spring phytoplankton biomass appear to be different among three sampling stations, suggesting a possibly more important role of local-scale forcing than large-scale forcing on phytoplankton dynamics at each station. The interannual variability of seasonal bloom progression derived from considering all three stations together captured ecologically meaningful, seasonally co-occurring bloom patterns which were primarily constrained by water-column stability strength. Our findings highlight a coupled link between phytoplankton and physical and climate dynamics along the coastal WAP, understanding of which is crucial in predicting overall WAP food web responses to climate change and variability.

Description: Glacial meltwater discharge from Antarctica is a key influence on the marine environment, impacting ocean circulation, sea level, and productivity of the pelagic and benthic ecosystems. The responses elicited depend strongly on the characteristics of the meltwater releases, including timing, spatial structure and geochemical composition. Here we use isotopic tracers to reveal the time-varying pattern of meltwater during a discharge event from the Fourcade Glacier into Potter Cove, northern Antarctic Peninsula. The discharge is strongly dependent on local air temperature, and accumulates into an extremely thin, buoyant layer at the surface. This layer showed evidence of elevated turbidity, and responded rapidly to changes in atmospherically-driven circulation to generate a strongly pulsed outflow from the cove to the broader ocean. These characteristics contrast with those further south along the Peninsula, where strong glacial frontal ablation is driven oceanographically by intrusions of warm deep waters from offshore. The Fourcade Glacier switched very recently to being land-terminating; if retreat rates elsewhere along the Peninsula remain high and glacier termini progress strongly landward, the structure and impact of the freshwater discharges are likely to increasingly resemble the patterns elucidated here.

Description: The biomass of the benthic marine macroalgae from the inner Potter Cove was studied along a depth profile across different substrates during Antarctic summer. Macroalgal associations were identified by means of cluster analysis. Twenty-two species have been found in the study site, approximately half of the species present in the area. This paucity may be ex-plained by the strong preponderance of the brown algae Desmarestia anceps and D. menziesii, which are able to exclude other species by competition for light. The mean bio-mass of all macroalgae was 1390 g DW/m2 ± 1787 g DW/m2. Nine macroalgal asso-ciations were identified with different preferences for depth, substrate and the degree of expo-sure. Overall, there was a tendency of macroalgae to grow on fine substrates with increasing depth. Species rich-ness decreased at 20m depth, probably due to limiting light conditions. The results are discussed with respect to previ-ous studies in East and West Antarctica.

Description: King George Island (KGI, Isla 25 de Mayo) is located within one of the most rapidly warming regions on Earth at the north-western tip of the Antarctic Peninsula. Since 1991 hydrographical characteristics and phytoplankton dynamics were monitored at two stations in Potter Cove, a fjord-like environment on the south-eastern KGI coastline. Seawater temperature and salinity, total suspended particulate matter (TSPM) and chlorophyll-a (Chl-a, a proxy for phytoplankton biomass) concentrations were measured in summer and winter over a 19 year period, together with local air temperature. Mean air temperatures rose by 0.39 and 0.48 ºC per decade in summer and winter, respectively. Positive anomalies characterised wind speeds during the decade between the mid ’90 and the mid 2000 years, whereas negative anomalies were observed from 2004 onwards. Day of sea ice formation and retreat, based on satellite data, did not change, although total sea ice cover diminished during the studied period. Surface water temperature increased during summer (0.36 ºC per decade), whereas no trend was observed in salinity. Summer Chl-a concentrations were around 1 mg m-3 Chl-a with no clear trend throughout the study period. However, summer Chl-a correlates positively with water column stratification, which in turn resulted from high air temperature and lower salinity in front of the melting glacier. TSPM increased in surface waters of the inner cove during the spring-summer months. The Southern Annular Mode (SAM) climate signal was apparent in the fluctuating interannual pattern of the hydrographic variables in the outer Potter Cove and bottom waters whereas surface hydrography was strongly governed by the local forcing of glacier melt. The results show that global trends have significant effects on local hydrographical and biological conditions in the coastal marine environments of Western Antarctica.

Description: A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with apotential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one ormore climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (〈1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to 〈1% for fourand five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.

Description: The west Antarctic Peninsula (WAP) region has undergone significant changes in temperature and seasonal ice dynamics since the mid-twentieth century, with strong impacts on the regional ecosystem, ocean chemistry and hydrographic properties. Changes to these long-term trends of warming and sea ice decline have been observed in the 21st century, but their consequences for ocean physics, chemistry and the ecology of the high-productivity shelf ecosystem are yet to be fully established. The WAP shelf is important for regional krill stocks and higher trophic levels, whilst the degree of variability and change in the physical environment and documented biological and biogeochemical responses make this a model system for how climate and sea ice changes might restructure high-latitude ecosystems. Although this region is arguably the best-measured and best-understood shelf region around Antarctica, significant gaps remain in spatial and temporal data capable of resolving the atmosphere-ice-ocean-ecosystem feedbacks that control the dynamics and evolution of this complex polar system. Here we summarise the current state of knowledge regarding the key mechanisms and interactions regulating the physical, biogeochemical and biological processes at work, the ways in which the shelf environment is changing, and the ecosystem response to the changes underway. We outline the overarching cross-disciplinary priorities for future research, as well as the most important discipline-specific objectives. Underpinning these priorities and objectives is the need to better-define the causes, magnitude and timescales of variability and change at all levels of the system. A combination of traditional and innovative approaches will be critical to addressing these priorities and developing a co-ordinated observing system for the WAP shelf, which is required to detect and elucidate change into the future.